1. Field of the Invention
The present invention relates to a sintered polycrystalline diamond (PCD) composite for use in rock drilling, machining of wear resistant metals, and other operations which require the high abrasion resistance or wear resistance of a diamond surface. Specifically, this invention relates to such bodies which comprise a PCD layer attached to a cemented metal carbide substrate via processing at ultrahigh pressures and temperatures.
2. Prior Art
PCD compacts have been used for industrial applications including rock drilling and metal machining for many years. One of the factors limiting the success of PCD is the strength of the bond between the polycrystalline diamond layer and the sintered metal carbide substrate. For example, analyses of the failure mode for drill bits used for deep hole rock drilling show that in approximately 33 percent of the cases, bit failure or wear is caused by delamination of the diamond from the metal carbide substrate.
U.S. Pat. No. 3,745,623 (reissue U.S. Pat. No. 32,380) teaches the attachment of diamond to tungsten carbide support material. This, however, results in a cutting tool with a relatively low impact resistance. FIG. 1, which is a perspective drawing of this prior art composite, shows that there is a very abrupt transition between the metal carbide support and the polycrystalline diamond layer. Due to the differences in the thermal expansion of diamond in the PCD layer and the binder metal used to cement the metal carbide substrate, there exists a stress in excess of 200,000 psi between these two layers. The force exerted by this stress must be overcome by the extremely thin layer of cobalt which is the binding medium that holds the PCD layer to the metal carbide substrate. Because of the very high stress between the two layers, which is distributed over a flat narrow transition zone, it is relatively easy for the compact to delaminate in this area upon impact. Additionally, it has been known that declaminations can also occur on heating or other disturbances aside from impact.
One solution to this problem is proposed in the teaching of U.S. Pat. No. 4,604,106. This patent utilizes one or more transitional layers incorporating powdered mixtures with various percentages of diamond, tungsten carbide, and cobalt to distribute the stress caused by the difference in thermal expansion over a larger area. A problem with this solution is that "sweep-through" of the metallic catalyst sintering agent is impeded by the free cobalt and the cobalt cemented carbide in the mixture.
U.S. Pat. No. 4,784,023 teaches the grooving of polycrystalline diamond substrates but does not teach the use of patterned substrate designed to uniformly reduce the stress between the polycrystalline diamond layer and the substrate support layer. In fact, this patent specifically mentions the use of undercut (or dovetail) portions of substrate grooves, which contributes to increased localized stress and is strictly forbidden by the present invention. FIG. 2 shows the region of highly concentrated stresses that results from fabricating polycrystalline diamond composites with substrates that are grooved in a dovetail manner. Instead of reducing the stress between the polycrystalline diamond layer and the metallic substrate, this actually makes the situation much worse. This is because the larger volume of metal at the top of the ridge will expand and contract during heating cycles to a greater extent than the polycrystalline diamond, forcing the composite to fracture at locations 1 and 2 shown in the drawing.
The disadvantage of using relatively few parallel grooves with planar side walls is that the stress again becomes concentrated along the top and the base of each groove and results in significant cracking of the metallic substrate and the diamond layer along the edges of the top and the bottom of the groove. This cracking 3 is shown in FIG. 3. As a result, construction of a polycrystalline diamond cutter following the teachings provided by U.S. Pat. No. 4,784,023 is not suitable for cutting applications where repeated high impact forces are encountered, such as in percussive drilling, nor in applications where extreme thermal shock is a consideration.
U.S. Pat. No. 4,592,433, which teaches grooving substrates, is not applicable to the present invention since these composites do not have a solid diamond table across the entire top surface of the substrate, and thus are not subjected to the same type of delamination failure. With the top layer of diamond not covering the entire surface, these composites cannot compete in the harsh abrasive application areas with the other prior art and present invention compacts mentioned in this patent application.
U.S. Pat. No. 4,629,373 describes the formation of various types of irregularities upon a polycrystalline diamond body without an attached substrate. The purpose of these irregularities is to increase the surface area of the diamond and to provide mechanical interlocking when the diamond is later brazed to a support or placed in a metal matrix. This patent specifically mentions that stress between the polycrystalline diamond and metal substrate support is a problem that results from manufacturing compacts by a one-step process. It, therefore, suggests that polycrystalline diamond bodies with surface irregularities be attached to support matrices in a second step after fabrication at ultra-high pressures and temperatures. This type of bond is, unfortunately, of significantly lower strength than that of a bond produced between diamond and substrate metals under diamond stable conditions. Therefore, compacts made by this process cannot be used in high impact applications or other applications in which considerable force is placed upon the polycrystalline diamond table.
U.S. Pat. No. 5,011,515 describes the formation of various irregularities which are pyramidal in shape on a substrate surface such that the spacing between these irregularities being greater at the base than at the top. See FIG. 4. Although stresses between the diamond and the metal carbide support is spread over a large area comparing with the prior art cutting element. Fruschour failed to achieve the goal of uniformly distributing the stresses over the entire region. The stresses at the sharp points of the pyramidal-shaped irregulars would be substantially increased which may lead to delamination and cracking failure between the diamond and the metal carbide substrate and cracking failure within the cutting element.
U.S. Pat. No. 5,351,772 issued to Smith teaches a cutting element comprising a PDC diamond table bonded to a tungsten carbide substrate having lands thereon spaced about the perimeter of the substrate. The diamond table depth exceed the height of the substrate lands so that alldiamond cutting surface is present. See FIG. 5. Like Frushour, Smith also fails to teach uniformly spreading the stresses between the diamond and carbide support. The residual stresses would be increased at the sharp points which would lead to delamination and cracking failure within the cutting element.
It would be desirable to have a composite compact wherein the stress between the diamond and metal carbide substrate could be uniformly spread over a larger area and the attachment between the diamond and metal carbide strengthened such that the impact resistance of the composite tool is improved without any loss of diamond-to-diamond bonding that results from efficient sweep-through of the catalyst sintering metal.